USQ astrophysicists make surprising, ancient find

THE discovery of a planet by University of Southern Queensland researchers with a highly eccentric orbit around an ancient star could help us understand more about how planetary systems form and evolve over time.

The newly discovered world, named HD76920b, is unique as it orbits an ancient star more than two billion years older than the Sun.

At its furthest, it orbits almost twice as far from its star as Earth does from the Sun.

These findings will be published in the Astronomical Journal and is a culmination of seven years of work by research lead Associate Professor Rob Wittenmyer and co-authors USQ Associate Professor Jonti Horner, PhD student Jake Clark and Associate Professor Stephen Kane from the University of California.

"We don't know why the orbit is so eccentric but we have a few ideas," Ass Prof Horner said.

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"Maybe the system had a few planets on circular orbits, and then became unstable. This planet flung the others out to the depths of space, leaving it alone, on a new, eccentric orbit.

"Alternatively, maybe the star has an unseen companion - perhaps it is a binary. Then the distant companion could have stirred up the orbit of the planet, leaving it where we see it today.

"Questions like these are part of the joy of science. It's amazing to find something we don't yet understand, as it shows there's still so much to learn."

A gaseous planet, HD76920b will change shape as it swings past its star, stretched by its enormous gravity.

These tides would be far greater than any experienced on Earth.

Ass Prof Wittenmyer said as was always the case in astronomy, more observations were needed to truly understand the life story of this peculiar planet.

"Even now, 20 years into the "exoplanet era" and with more than 3000 planets known, this discovery shows that the universe can still surprise us," he said.